Lesson No 26

1. the 2-nd division of the fifth cranial nerve, areas of distribution. Autonomic nerves of the head

2. the 3-d division of of the fifth cranial nerve, areas of distribution. Autonomic ganglia of the head

3. the 7-th, 11-th and 12-th cranial nerves

 

Lesson No 26

Theme 1. the 2-nd division of the fifth cranial nerve, areas of distribution. Autonomic nerves of the head

Maxillary nerve passes through the rotundum foramen and reaches the pterygopalatine fossa, where ramifies on three branches: infraorbital nerve, zygomatic nerve and ganglionic branches to pterygopalatine ganglion.

 Infraorbital nerve passes through the inferior orbital fissura enters into orbite, where lies on its lower wall, passes in infraorbital fissura and infraorbital sulcus and canal. Nerve passes into canine fossa, forming pes anserinus minor’. There are inferior palpebral, external nasal and superior labial nerves that innervate skin from medial eye corner to mouth corner. Superior alveolar nerves (posterior, middle and inferior) start from infraorbital nerve in maxilla. They innervate mucous membrane of the maxillary (Haymori) sinus and form superior dental plexus. The last gives off the superior dental nerves and superior gingival branches of the upper jaw.

Zygomatic nerve passes through the inferior orbital fissura entering orbite. Then it passes into zygomaticoorbital foramen and divided into zygomaticofacial and zygomaticotemporal sensory branches for skin of face and temporal region. Zygomatic nerve carries postganglionic parasympathetic fibres from pterygopalatine ganglion and gives off them to lacrimal nerve. Parasympathetic fibres provide secretory innervation of the lacrimal gland.

The ganglionic branches start from maxillary nerve and pass to pterygopalatine ganglion. Postganglionic branches include greater palatine nerve and lesser palatine nerve that pass through the greater palatine canal and lesser palatine foramens, innervating mucous membrane of the hard and soft palatine.


image778

Distribution of the maxillary and mandibular nerves, and the submandibular ganglion.

 

The posterior nasal (medial and lateral) nerves pass through the sphenopalatine foramen pass into nasal cavity, where innervate mucous membrane of the nasal cavity. Nasopalatine nerve (Scarp’) start from the nasal branches and reach the mucous membrane of the hard palatine through the incisive canal. Postganglionic parasympathetic fibres from pterygopalatine ganglion are in composition of these nerves.

Nuclei of the V-XII Cranial Nerves

No

Name

Nucleus

Function

Location

V

Trigeminal

Motor nucleus

mesencephalic, pontine, spinal nuclei

Motor

sensory

Pons,

mesencephalon, pons, spinal cord

VI

Abducent

Abducent

Motor

Colliculus facialis (superficially)

VII

Facial

Facial (forms genu)

nucleus of the tractus solitarius

superior salivatory

Motor

Sensory

 

parasympathetic

Colliculus facialis (deep),

Pons

 

VIII

Vestibulo-cochlear

Superior, inferior, medial and lateral vestibular (4),

Ventral and dorsal cochlear (2)

All sensory

Vestibular area

 

lateral recess

IX

Glosso-pharyngeal

Ambiguus

nucleus of the tractus solitarius

Inferior salivatory

Motor

Sensory

 

Parasympathetic

Medial eminence

Medulla oblongata

X

Vagus

Ambiguus

nucleus of the tractus solitarius

dorsal nucleus

Motor

Sensory

 

parasympathetic

Medial eminence

Medulla oblongata

Trigone of the vagus nerve

XI

Accessory

Cranial nucleus,

spinal nucleus

Motor

Motor

Medial eminence

spinal cord

XII

Hypoglossal

hypoglossal

Motor

Trigone of the hypoglossal nerve

 

The Maxillary Nerve (n. maxillaris; superior maxillary nerve) (778), or second division of the trigeminal, is a sensory nerve. It is intermediate, both in position and size, between the ophthalmic and mandibular. It begins at the middle of the semilunar ganglion as a flattened plexiform band, and, passing horizontally forward, it leaves the skull through the foramen rotundum, where it becomes more cylindrical in form, and firmer in texture. It then crosses the pterygopalatine fossa, inclines lateralward on the back of the maxilla, and enters the orbit through the inferior orbital fissure; it traverses the infraorbital groove and canal in the floor of the orbit, and appears upon the face at the infraorbital foramen. 131 At its termination, the nerve lies beneath the Quadratus labii superioris, and divides into a leash of branches which spread out upon the side of the nose, the lower eyelid, and the upper lip, joining with filaments of the facial nerve.

Branches.—Its branches may be divided into four groups, according as they are given off in the cranium, in the pterygopalatine fossa, in the infraorbital canal, or on the face.

In the Cranium……………

Middle meningeal.

In the Pterygopalatine Fossa…

Zygomatic.

Sphenopalatine.

Posterior superior alveolar.

In the Infraorbital Canal………

Anterior superior alveolar.

Middle superior alveolar.

On the Face…………………

Inferior palpebral.

External nasal.

Superior labial.

The Middle Meningeal Nerve (n. meningeus medius; meningeal or dural branch) is given off from the maxillary nerve directly after its origin from the semilunar ganglion; it accompanies the middle meningeal artery and supplies the dura mater.

  The Zygomatic Nerve (n. zygomaticus; temporomalar nerve; orbital nerve) arises in the pterygopalatine fossa, enters the orbit by the inferior orbital fissure, and divides at the back of that cavity into two branches, zygomaticotemporal and zygomaticofacial.

  The zygomaticotemporal branch (ramus zygomaticotemporalis; temporal branch) runs along the lateral wall of the orbit in a groove in the zygomatic bone, receives a branch of communication from the lacrimal, and, passing through a foramen in the zygomatic bone, enters the temporal fossa. It ascends between the bone, and substance of the Temporalis muscle, pierces the temporal fascia about 2.5 cm. above the zygomatic arch, and is distributed to the skin of the side of the forehead, and communicates with the facial nerve and with the aurićulotemporal branch of the mandibular nerve. As it pierces the temporal fascia, it gives off a slender twig, which runs between the two layers of the fascia to the lateral angle of the orbit.

  The zygomaticofacial branch (ramus zygomaticofacialis; malar branch) passes along the infero-lateral angle of the orbit, emerges upon the face through a foramen in the zygomatic bone, and, perforating the Orbicularis oculi, supplies the skin on the prominence of the cheek. It joins with the facial nerve and with the inferior palpebral branches of the maxillary.

  The Sphenopalatine Branches (nn. sphenopalatini), two in number, descend to the sphenopalatine ganglion.

  

The Posterior Superior Alveolar Branches (rami alveolares superiores posteriores; posterior superior dental branches) arise from the trunk of the nerve just before it enters the infraorbital groove; they are generally two in number, but sometimes arise by a single trunk. They descend on the tuberosity of the maxilla and give off several twigs to the gums and neighboring parts of the mucous membrane of the cheek. They then enter the posterior alveolar canals on the infratemporal surface of the maxilla, and, passing from behind forward in the substance of the bone, communicate with the middle superior alveolar nerve, and give off branches to the lining membrane of the maxillary sinus and three twigs to each molar tooth; these twigs enter the foramina at the apices of the roots of the teeth.

  The Middle Superior Alveolar Branch (ramus alveolaris superior medius; middle superior dental branch), is given off from the nerve in the posterior part of the infraorbital canal, and runs downward and forward in a canal in the lateral wall of the maxillary sinus to supply the two premolar teeth. It forms a superior dental plexus with the anterior and posterior superior alveolar branches.

 

 

 

The Anterior Superior Alveolar Branch (ramus alveolaris superior anteriores; anterior superior dental branch), of considerable size, is given off from the nerve just before its exit from the infraorbital foramen; it descends in a canal in the anterior wall of the maxillary sinus, and divides into branches which supply the incisor and canine teeth. It communicates with the middle superior alveolar branch, and gives off a nasal branch, which passes through a minute canal in the lateral wall of the inferior meatus, and supplies the mucous membrane of the anterior part of the inferior meatus and the floor of the nasal cavity, communicating with the nasal branches from the sphenopalatine ganglion.

 

image779
Alveolar branches of superior maxillary nerve and sphenopalatine ganglion.

 

  The Inferior Palpebral Branches (rami palpebrales inferiores; palpebral branches) ascend behind the Orbicularis oculi. They supply the skin and conjunctiva of the lower eyelid, joining at the lateral angle of the orbit with the facial and zygomaticofacial nerves.

  The External Nasal Branches (rami nasales externi) supply the skin of the side of the nose and of the septum mobile nasi, and join with the terminal twigs of the nasociliary nerve.

  The Superior Labial Branches (rami labiales superiores; labial branches), the largest and most numerous, descend behind the Quadratus labii superioris, and are distributed to the skin of the upper lip, the mucous membrane of the mouth, and labial glands. They are joined, immediately beneath the orbit, by filaments from the facial nerve, forming with them the infraorbital plexus.

 

Sphenopalatine Ganglion (ganglion of Meckel) (780).

 

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—The sphenopalatine ganglion, the largest of the sympathetic ganglia associated with the branches of the trigeminal nerve, is deeply placed in the pterygopalatine fossa, close to the sphenopalatine foramen. It is triangular or heart-shaped, of a reddish-gray color, and is situated just below the maxillary nerve as it crosses the fossa. It receives a sensory, a motor, and a sympathetic root.

  Its sensory root is derived from two sphenopalatine branches of the maxillary nerve; their fibers, for the most part, pass directly into the palatine nerves; a few, however, enter the ganglion, constituting its sensory root. Its motor root is probably derived from the nervus intermedius through the greater superficial petrosal nerve and is supposed to consist in part of sympathetic efferent (preganglionic) fibers from the medulla. In the sphenopalatine ganglion they form synapses with neurons whose postganglionic axons, vasodilator and secretory fibers, are distributed with the deep branches of the trigeminal to the mucous membrane of the nose, soft palate, tonsils, uvula, roof of the mouth, upper lip and gums, and to the upper part of the pharynx. Its sympathetic root is derived from the carotid plexus through the deep petrosal nerve. These two nerves join to form the nerve of the pterygoid canal before their entrance into the ganglion.

image780

The sphenopalatine ganglion and its branches.

  The greater superficial petrosal nerve (n. petrosus superficialis major; large superficial petrosal nerve) is given off from the genicular ganglion of the facial nerve; it passes through the hiatus of the facial canal, enters the cranial cavity, and runs forward beneath the dura mater in a groove on the anterior surface of the petrous portion of the temporal bone. It then enters the cartilaginous substance which fills the foramen lacerum, and joining with the deep petrosal branch forms the nerve of the pterygoid canal.

  The deep petrosal nerve (n. petrosus profundus; large deep petrosal nerve) is given off from the carotid plexus, and runs through the carotid canal lateral to the internal carotid artery. It then enters the cartilaginous substance which fills the foramen lacerum, and joins with the greater superficial petrosal nerve to form the nerve of the pterygoid canal.

  The nerve of the pterygoid canal (n. canalis pterygoidei [Vidii]; Vidian nerve), formed by the junction of the two preceding nerves in the cartilaginous substance which fills the foramen lacerum, passes forward, through the pterygoid canal, with the corresponding artery, and is joined by a small ascending sphenoidal branch from the otic ganglion. Finally, it enters the pterygopalatine fossa, and joins the posterior angle of the sphenopalatine ganglion.

 

Branches of Distribution.—These are divisible into four groups, viz., orbital, palatine, posterior superior nasal, and pharyngeal.

  The orbital branches (rami orbitales; ascending branches) are two or three delicate filaments, which enter the orbit by the inferior orbital fissure, and supply the periosteum. According to Luschka, some filaments pass through foramina in the frontoethmoidal suture to supply the mucous membrane of the posterior ethmoidal and sphenoidal sinuses.

  The palatine nerves (nn. palatini; descending branches) are distributed to the roof of the mouth, soft palate, tonsil, and lining membrane of the nasal cavity. Most of their fibers are derived from the sphenopalatine branches of the maxillary nerve. They are three in number: anterior, middle, and posterior.

  The anterior palatine nerve (n. palatinus anterior) descends through the pterygopalatine canal, emerges upon the hard palate through the greater palatine foramen, and passes forward in a groove in the hard palate, nearly as far as the incisor teeth. It supplies the gums, the mucous membrane and glands of the hard palate, and communicates in front with the terminal filaments of the nasopalatine nerve. While in the pterygopalatine canal, it gives off posterior inferior nasal branches, which enter the nasal cavity through openings in the palatine bone, and ramify over the inferior nasal concha and middle and inferior meatuses; at its exit from the canal, a palatine branch is distributed to both surfaces of the soft palate.

  The middle palatine nerve (n. palatinus medius) emerges through one of the minor palatine canals and distributes branches to the uvula, tonsil, and soft palate. It is occasionally wanting.

  The posterior palatine nerve (n. palatinus posterior) descends through the pterygopalatine canal, and emerges by a separate opening behind the greater palatine foramen; it supplies the soft palate, tonsil, and uvula. The middle and posterior palatine join with the tonsillar branches of the glossopharyngeal to form a plexus (circulus tonsillaris) around the tonsil.

  The posterior superior nasal branches (rami nasales posteriores superiores) are distributed to the septum and lateral wall of the nasal fossa. They enter the posterior part of the nasal cavity by the sphenopalatine foramen and supply the mucous membrane covering the superior and middle nasal conchæ, the lining of the posterior ethmoidal cells, and the posterior part of the septum. One branch, longer and larger than the others, is named the nasopalatine nerve. It enters the nasal cavity through the sphenopalatine foramen, passes across the roof of the nasal cavity below the orifice of the sphenoidal sinus to reach the septum, and then runs obliquely downward and forward between the periosteum and mucous membrane of the lower part of the septum. It descends to the roof of the mouth through the incisive canal and communicates with the corresponding nerve of the opposite side and with the anterior palatine nerve. It furnishes a few filaments to the mucous membrane of the nasal septum.

  The pharyngeal nerve (pterygopalatine nerve) is a small branch arising from the posterior part of the ganglion. It passes through the pharyngeal canal with the pharyngeal branch of the internal maxillary artery, and is distributed to the mucous membrane of the nasal part of the pharynx, behind the auditory tube.

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Theme 2. the 3-d division of of the fifth cranial nerve, areas of distribution. Autonomic ganglia of the head

Mandibular nerve carries both the motor and sensory fibres. After passing out from ovale foramen mandibular nerve gives off the motor branches that innervate all 4 masticatory muscles, also velli palatine tensor muscle and nerve tensor of tympanic membrane muscle. Sensory branches of the mandibular nerve: buccal nerve, auriculotemporal nerve, lingual nerve infeior alveolar nerve and meningeal branches.

Buccal nerve transfixes a buccinator muscle and innervates mucous membrane of the cheek and also mouth corner skin.

Auriculotemporal nerve begins by two rootlets that envelop a middle meningeal artery, and then unite into one trunk, which transfixes parotid gland, innervating it and skin of temporal area, also, the auricle. Postganglionic parasympathetic fibres from otic ganglion pass in composition of this nerve, which provide a secretory innervation of parotid gland.

Lingual nerve passes on internal surface of lower jaw under mucous membrane of the mouth cavity and enters into lower part of tongue, providing a general sensory innervation of the anterior 2/3 part and sensory innervation sublingual and submandibular salivary glands. Chorda tympani (from 7th cranial nerve), which contains the gustatory (tasting) and secretory (parasympathetic) fibres. Gustatory fibres innervate of tasting buds on mucous membrane of the anterior 2/3 part of the tongue, and secretory (parasympathetic) enter in to submandibular and sublingual parasympatheticих ganglia. The postganglionic fibres from these ganglia provide a secretory innervation the same name - submandibular and sublingual salivary glands.

Inferior alveolar nerve (mixed) has a motor branches that supply mylo-hyoid muscle and anterior belly of the digastric muscle. The sensory fibres enter into mandibular channel, where form inferior dental plexus, branches innervate the teeth and gums of lower jaw. From canal these fibres are passing out from bone as a mental nerve, which terminates in skin of lower lip and chin.

  The mandibular nerve (n. mandibulari supplies the teeth and gums of the mandible, the skin of the temporal region, the auricula, the lower lip, the lower part of the face, and the muscles of mastication; it also supplies the mucous membrane of the anterior two-thirds of the tongue. It is the largest of the three divisions of the fifth, and is made up of two roots: a large, sensory root proceeding from the inferior angle of the semilunar ganglion, and a small motor root (the motor part of the trigeminal), which passes beneath the ganglion, and unites with the sensory root, just after its exit through the foramen ovale. Immediately beneath the base of the skull, the nerve gives off from its medial side a recurrent branch (nervus spinosus) and the nerve to the Pterygoideus internus, and then divides into two trunks, an anterior and a posterior.

  The Nervus Spinosus (recurrent or meningeal branch) enters the skull through the foramen spinosum with the middle meningeal artery. It divides into two branches, anterior and posterior, which accompany the main divisions of the artery and supply the dura mater; the posterior branch also supplies the mucous lining of the mastoid cells; the anterior communicates with the meningeal branch of the maxillary nerve.

image781

Mandibular division of the trifacial nerve.

 The Internal Pterygoid Nerve (n. pterygoideus internus).—The nerve to the Pterygoideus internus is a slender branch, which enters the deep surface of the muscle; it gives off one or two filaments to the otic ganglion.

  The anterior and smaller division of the mandibular nerve receives nearly the whole of the fibers of the motor root of the nerve, and supplies the muscles of mastication and the skin and mucous membrane of the cheek. Its branches are the masseteric, deep temporal, buccinator, and external pterygoid.

  The Masseteric Nerve (n. massetericus) passes lateralward, above the Pterygoideus externus, in front of the temporomandibular articulation, and behind the tendon of the Temporalis; it crosses the mandibular notch with the masseteric artery, to the deep surface of the Masseter, in which it ramifies nearly as far as its anterior border. It gives a filament to the temporomandibular joint.

  The Deep Temporal Nerves (nn. temporales profundi) are two in number, anterior and posterior. They pass above the upper border of the Pterygoideus externus and enter the deep surface of the Temporalis. The posterior branch, of small size, is placed at the back of the temporal fossa, and sometimes arises in common with the masseteric nerve. The anterior branch is frequently given off from the buccinator nerve, and then turns upward over the upper head of the Pterygoideus externus. Frequently a third or intermediate branch is present.

  The Buccinator Nerve (n. buccinatorus; long buccal nerve) passes forward between the two heads of the Pterygoideus externus, and downward beneath or through the lower part of the Temporalis; it emerges from under the anterior border of the Masseter, ramifies on the surface of the Buccinator, and unites with the buccal branches of the facial nerve. It supplies a branch to the Pterygoideus externus during its passage through that muscle, and may give off the anterior deep temporal nerve. The buccinator nerve supplies the skin over the Buccinator, and the mucous membrane lining its inner surface.

 

External Pterygoid Nerve (n. pterygoideus externus).—The nerve to the Pterygoideus externus frequently arises in conjunction with the buccinator nerve, but it may be given off separately from the anterior division of the mandibular nerve. It enters the deep surface of the muscle.

  The posterior and larger division of the mandibular nerve is for the most part sensory, but receives a few filaments from the motor root. It divides into auriculotemporal, lingual, and inferior alveolar nerves.

  The Auriculotemporal Nerve (n. auriculotemporalis) generally arises by two roots, between which the middle meningeal artery ascends. It runs backward beneath the Pterygoideus externus to the medial side of the neck of the mandible. It then turns upward with the superficial temporal artery, between the auricula and condyle of the mandible, under cover of the parotid gland; escaping from beneath the gland, it ascends over the zygomatic arch, and divides into superficial temporal branches.

  The branches of communication of the auriculotemporal nerve are with the facial nerve and with the otic ganglion. The branches to the facial, usually two in number, pass forward from behind the neck of the mandible and join the facial nerve at the posterior border of the Masseter. The filaments to the otic ganglion are derived from the roots of the auriculotemporal nerve close to their origin.

  Its branches of distribution are:

Anterior auricular.

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Articular.

Branches to the external acoustic meatus.

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Parotid.

Superficial temporal.

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  The anterior auricular branches (nn. auriculares anteriores) are usually two in number; they supply the front of the upper part of the auricula, being distributed principally to the skin covering the front of the helix and tragus.

  The branches to the external acoustic meatus (n. meatus auditorii externi), two in number, enter the meatus between its bony and cartilaginous portions and supply the skin lining it; the upper one sends a filament to the tympanic membrane.

  The articular branches consist of one or two twigs which enter the posterior part of the temporomandibular joint.

  The parotid branches (rami parotidei) supply the parotid gland.

  The superficial temporal branches (rami temporales superficiales) accompany the superficial temporal artery to the vertex of the skull; they supply the skin of the temporal region and communicate with the facial and zygomaticotemporal nerves.

  The Lingual Nerve (n. lingualis) supplies the mucous membrane of the anterior two-thirds of the tongue. It lies at first beneath the Pterygoideus externus, medial to and in front of the inferior alveolar nerve, and is occasionally joined to this nerve by a branch which may cross the internal maxillary artery. The chorda tympani also joins it at an acute angle in this situation. The nerve then passes between the Pterygoideus internus and the ramus of the mandible, and crosses obliquely to the side of the tongue over the Constrictor pharyngis superior and Styloglossus, and then between the Hyoglossus and deep part of the submandibular gland; it finally runs across the duct of the submandibular gland, and along the tongue to its tip, lying immediately beneath the mucous membrane.

  Its branches of communication are with the facial (through the chorda tympani), the inferior alveolar and hypoglossal nerves, and the submandibular ganglion. The branches to the submandibular ganglion are two or three in number; those connected with the hypoglossal nerve form a plexus at the anterior margin of the Hyoglossus.

image782

Mandibular division of trifacial nerve, seen from the middle line. The small figure is an enlarged view of the otic ganglion

 

  Its branches of distribution supply the sublingual gland, the mucous membrane of the mouth, the gums, and the mucous membrane of the anterior two-thirds of the tongue; the terminal filaments communicate, at the tip of the tongue, with the hypoglossal nerve.

  The Inferior Alveolar Nerve (n. alveolaris inferior; inferior dental nerve)(782) is the largest branch of the mandibular nerve. It descends with the inferior alveolar artery, at first beneath the Pterygoideus externus, and then between the sphenomandibular ligament and the ramus of the mandible to the mandibular foramen. It then passes forward in the mandibular canal, beneath the teeth, as far as the mental foramen, where it divides into two terminal branches, incisive and mental.

  The branches of the inferior alveolar nerve are the mylohyoid, dental, incisive, and mental.

  The mylohyoid nerve (n. mylohyoideus) is derived from the inferior alveolar just before it enters the mandibular foramen. It descends in a groove on the deep surface of the ramus of the mandible, and reaching the under surface of the Mylohyoideus supplies this muscle and the anterior belly of the Digastricus.

  The dental branches supply the molar and premolar teeth. They correspond in number to the roots of those teeth; each nerve entering the orifice at the point of the root, and supplying the pulp of the tooth; above the alveolar nerve they form an inferior dental plexus.

  The incisive branch is continued onward within the bone, and supplies the canine and incisor teeth.

  The mental nerve (n. mentalis) emerges at the mental foramen, and divides beneath the Triangularis muscle into three branches; one descends to the skin of the chin, and two ascend to the skin and mucous membrane of the lower lip; these branches communicate freely with the facial nerve.

  Two small ganglia, the otic and the submaxillary, are connected with the mandibular nerve.

image783

The otic ganglion and its branches.

 

 

Otic Ganglion (ganglion oticum)(783).—The otic ganglion is a small, ovalshaped, flattened ganglion of a reddish-gray color, situated immediately below the foramen ovale; it lies on the medial surface of the mandibular nerve, and surrounds the origin of the nerve to the Pterygoideus internus. It is in relation, laterally, with the trunk of the mandibular nerve at the point where the motor and sensory roots join; medially, with the cartilaginous part of the auditory tube, and the origin of the Tensor veli palatini; posteriorly, with the middle meningeal artery.

 

Branches of Communication.—It is connected by two or three short filaments with the nerve to the Pterygoideus internus, from which it may obtain a motor, and possibly a sensory root. It communicates with the glossopharyngeal and facial nerves, through the lesser superficial petrosal nerve continued from the tympanic plexus, and through this nerve it probably receives a root from the glossopharyngeal and a motor root from the facial; its sympathetic root consists of a filament from the plexus surrounding the middle meningeal artery. The fibers from the glossopharyngeal which pass to the otic ganglion in the small superficial petrosal are supposed to be sympathetic efferent (preganglionic) fibers from the dorsal nucleus or inferior salivatory nucleus of the medulla. Fibers (postganglionic) from the otic ganglion with which these form synapses are supposed to pass with the auriculotemporal nerve to the parotid gland. A slender filament (sphenoidal) ascends from it to the nerve of the Pterygoid canal, and a small branch connects it with the chorda tympani.

  Its branches of distribution are: a filament to the Tensor tympani, and one to the Tensor veli palatini. The former passes backward, lateral to the auditory tube; the latter arises from the ganglion, near the origin of the nerve to the Pterygoideus internus, and is directed forward. The fibers of these nerves are, however, mainly derived from the nerve to the Pterygoideus internus.

image784

Sensory areas of the head, showing the general distribution of the three divisions of the fifth nerve.

 

 

Submandibular Ganglion (ganglion submaxillare)(778).—The submandibular ganglion is of small size and is fusiform in shape. It is situated above the deep portion of the submandibular gland, on the hyoglossus, near the posterior border of the Mylohyoideus, and is connected by filaments with the lower border of the lingual nerve. It is suspended from the lingual nerve by two filaments which join the anterior and posterior parts of the ganglion. Through the posterior of these it receives a branch from the chorda tympani nerve which runs in the sheath of the lingual; these are sympathetic efferent (preganglionic) fibers from the facial nucleus or the superior salivatory nucleus of the medulla oblongata that terminate in the submandibular ganglion. The postganglionic fibers pass to the submandibular gland, it communicates with the sympathetic by filaments from the sympathetic plexus around the external maxillary artery.

  Its branches of distribution are five or six in number; they arise from the lower part of the ganglion, and supply the mucous membrane of the mouth and the duct of the submandibular gland, some being lost in the submandibular gland. The branch of communication from the lingual to the forepart of the ganglion is by some regarded as a branch of distribution, through which filaments pass from the ganglion to the lingual nerve, and by it are conveyed to the sublingual gland and the tongue.

 

Trigeminal Nerve Reflexes.—Pains referred to various branches of the trigeminal nerve are of very frequent occurrence, and should always lead to a careful examination in order to discover a local cause. As a general rule the diffusion of pain over the various branches of the nerve is at first confined to one only of the main divisions, and the search for the causative lesion should always commence with a thorough examination of all those parts which are supplied by that division; although in severe cases pain may radiate over the branches of the other main divisions. The commonest example of this condition is the neuralgia which is so often associated with dental caries—here, although the tooth itself may not appear to be painful, the most distressing referred pains may be experienced, and these are at once relieved by treatment directed to the affected tooth.

  Many other examples of trigeminal reflexes could be quoted, but it will be sufficient to mention the more common ones. Dealing with the ophthalmic nerve, severe supraorbital pain is commonly associated with acute glaucoma or with disease of the frontal or ethmoidal air cells. Malignant growths or empyema of the maxillary antrum, or unhealthy conditions about the inferior conchæ or the septum of the nose, are often found giving rise to “second division” neuralgia, and should be always looked for in the absence of dental disease in the maxilla.

  It is on the mandibular nerve, however, that some of the most striking reflexes are seen. It is quite common to meet with patients who complain of pain in the ear, in whom there is no sign of aural disease, and the cause is usually to be found in a carious tooth in the mandible. Moreover, with an ulcer or cancer of the tongue, often the first pain to be experienced is one which radiates to the ear and temporal fossa, over the distribution of the auriculotemporal nerve.

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Theme 3. the 7-th, 11-th and 12-th cranial nerves

VII Facial nerve consists of 1- proper facial nerve, which has fibers starting from motor nucleus in depth of facial colliculus in rhomboid fossa, and 2- intermediate nerve, which has a fibers of sensory nucleus of solitarius tract and parasympathetic - superior salivatory nucleus.

2 roots

·         Motor

o    Origin: From facial nucleus

o    Projects to: Facial muscles; Stapedius; Digastric & Stylohyoid

·         Nervus intermedius

o    Sensory afferents

o    Origin: Cell bodies in geniculate nucleus

o    Projections

§  Skin: To spinal nucleus of cranial nerve V

§  Taste: To nucleus tractus solitarius

o    Preganglionic parasympathetics

o    From superior salivatory nucleus

 Branches

·         Large petrosal: Lacrimation & Salivation; Parasympathetic

·         Nerve to stapedius muscle: Origin in tympanic canal

·         Chorda tympani

o    Joins lingual nerve

o    Taste in anterior 2/3 of tongue

o    Preganglionic Parasympathetic fibers

o    To submandibular ganglion

o    To sublingual & submaxillary glands

·         Sensory auricular branch

o    Sensation

o    Posterior external auditory canal

o    Inferior ear pinna

o    Some axons may arise from vagus (Arnold's nerve)

·         Motor innervation: Facial muscles (Facial expression)

Facial nerve: Anatomy

·         Neighboring nerves

o    VI: Internal genu of VII nerve curves around VI nerve nucleus

o    VIII: Accompanies VII nerve in internal acoustic canal

EMG: Motor units vs Limbs

·         Amplitude: Smaller

·         Duration: Shorter

·         Firing rate: Faster

External links

·         USUHS

o    Brainstem anatomy

o    Nerve anatomy

Facial nerve passes through facial canal, gives off motor branch for stapedius muscle, then exits from skull through the stylomastoid foramen and innervates posterior auricular, stylohyoid muscles and posterior belly of digastric muscle. Facial nerve enters into thickness of parotid salivary glands (but does not innervate it!) and forms there parotid plexus. Last gives off the motor branches which innervate facial expression (mimetic) muscles. There are: temporal branches (supply auricular, orbicularis oculi and occipitofrontalis muscles), zygomatic branches (they supply zygomatic major and orbicularis oculi muscles), buccal branches (supply zygomatic major and minor, levator labii superioris, buccinator, orbicularis oris, nasalis,  and risorius muscles), marginal mandibulae branch (supplies depressor anguli oris and depressor labii inferioris, mentalis muscles) and cervical branch (for the platisma).

Intermediate nerve has two divisions: Nervus petrosus major and Chorda tympani.

The facial nerve (788, 790) consists of a motor and a sensory part, the latter being frequently described under the name of the nervus intermedius (pars intermedii of Wrisberg)(788). The two parts emerge at the lower border of the pons in the recess between the olive and the inferior peduncle, the motor part being the more medial, immediately to the lateral side of the sensory part is the acoustic nerve.

The facial nerve is one of those cranial nerves that gives a headache just trying to think about it.

Although at first glance it is a motor nerve to facial expression, which begins as a trunk and emerges from the parotid gland as five branches (mnemonic here), it has taste and parasympathetic fibres which relay in complicated ways. It is therefore best to take it one step at a time.

Nuclei and brainstem tracts

Three brainstem nuclei contribute to the facial nerve; one motor, one secretomotor, and one sensory.

·                     facial nerve nucleus in the pons. As the motor fibres of the facial nerve loop posteriorly over the abducens nerve nucleus, they form the facial colliculus in the floor of fourth ventricle.

·                     superficial salivary nucleus, next to the facial nucleus supplies secretomotor parasympathetic fibres.

·                     nucleus of tractus solitarius, lateral to the dorsal nucleus of the vagus nerve, supplies taste fibres that eventually end up in the chorda tympani.

General course

The facial nerve has six named segments:

1.                intracranial (cisternal) segment

2.                meatal segment (internal auditory canal) - 8 mm - zero branches

3.                labyrinthine segment (IAC to geniculate ganglion) - 3 - 4mm - 3 branches (from geniculate ganglion)

4.                tympanic segment (from geniculate ganglion to pyramidal eminence) - 8 - 11mm - zero branches

5.                mastoid segment (from pyramidal eminence to stylomastoid foramen) - 8 - 14mm - 3 branches

6.                extratemporal segment (from stylomastoid foramen to division into major branches) 15 - 20mm - 9 branches

Cisternal segment

The nerve emerges immediately beneath the pons, lateral to the abducens nerve and medial to the vestibulocochlear nerve, and is joined by the nervus intermedius which has emerged lateral to the main trunk. Together the two travel through the cerebellopontine angle to the internal acoustic meatus

Meatal segment

Having been joined by the nervus intermedius they are located in the superior upper quadrant, above the falciform crest and anterior to Bill's bar.

Labyrinthine segment

As the facial nerve and nervus intermedius pass through the anterior superior quadrant of the internal acoustic meatus it enters the Fallopian canal, passing anterolaterally between and superior to the cochlea (anterior) and vestibule (posterior), and then runs back posteriorly at the geniculate ganglion (where the nervus intermedius joins the facial nerve, and where fibers for taste synapse - see below). It is here that three branches originate: the greater superfical petrosal nerve, the lesser petrosal nerve and the external petrosal nerve.

The labyrinthine segment is the shortest only measuring 3 to 4 mm. It is also the narrowest and the most susceptible to vascular compromise (see below).

Tympanic segment

As the nerve passes posteriorly from the geniculate ganglion it becomes the tympanic segment (8-11 mm in length), and is immediately beneath the lateral semicircular canal in the medial wall of the middle ear cavity. The bone of the Fallopian canal is often dehiscent in the area of the oval window in 25-55% of postmortem specimens, having mucosa in direct contact with the nerve. The nerve pass posterior to the cochleariform process, tensor tympani and oval window. Just distal to the pyramidal eminence the nerve makes a second turn (second genu) passing vertically downwards as the mastoid segment.

The tympanic segment has no branches.

Mastoid segment

The mastoid segment, measuring 8 to 14mm in length, extends from the second genu to the stylomastoid foramen, through what is confusingly referred to as the fallopian canal. It gives off three branches:

1.                nerve to stapedius

2.                chorda tympani - terminal branch of the nervus intermedius carrying both secretomotor fibres to the submandibular gland and sublingual gland and taste to the anterior two thirds of the tongue.

3.                nerve from the auricular branch of the vagus nerve (CN X) - pain fibers to the posterior part of the external acoustic meatus hitchhike from the jugular foramen.

Extratemporal segment

As the nerve exits the stylomastoid foramen, it gives off a sensor branch which supplies part of the external acoustic meatus and tympanic membrane. It then passes between the posterior belly of the digastric muscle and the stylohyoid muscle and enters the parotid gland. Lying between the deep and superfical lobes of the gland the nerve divides into to main branches at the pes anserinus (duck foot) - a superior temporofacial and and inferior cervicofacial branches. From the anterior border of the gland, five branches emerge; temporal, zygomatic, buccal, mandibular (marginal) and cervical.

The temporal branch runs with the superficial musculoaponeurotic system (SMAS) over the zygomatic arch. This branch is at risk during surgery in this region. To avoid damage procedures should be deep to the SMAS (e.g. zygomatic fracture repairs).

The mandibular branch, in 80% of cases, runs along the lower border of the mandible (thus also referred to as marginal branch). In 20% of cases however it can be up to 2cm below the margin of the mandible. It is crucial to be aware of this if surgery in the submandibular region is being performed. Injury to this branch will result in paralysis of mouth depressors.

Taste

Taste fibers to the anterior two thirds of the tongue originate in the nucleus of the tractus solitarius (NTS), travel in the nervus intermedius (preganglionic) where they join the facial nerve at the geniculate ganglion and synpase. Postganglionic fibers travel with the facial nerve and are given off as the chorda tympani, which eventually joins the lingual nerve (branch of the trigeminal nerve (CN V)).

Parasympathetic

Preganglionic fibres originate in the superior salivary nucleus and join the facial nerve at the geniculate ganglion having traveled with the nervus intermedius. They do not synapse in the ganglion, but rather pass through to be distributed between:

1.                greater superficial petrosal nerve anastamosing in the pterygopalatine ganglion and supplying the lacrimal gland

2.                lesser petrosal nerve anastamosing in the otic ganglion and supplying the parotid gland (along with fibers from the inferior salivary nucleus which arrive via the glossopharyngeal nerve (CN IX) supply to the tympanic plexus)

3.                chorda tympani anastamosing in the submandibular ganglion and supplying the submandibular gland and sublingual gland

Blood supply

The facial nerve receives its arterial supply from three main sources:

1.                labyrinthine artery - a branch of the AICA, supplies the meatal segment. It is supplemented by direct twigs in the cisternal postion, directly from the AICA.

2.                superficial petrosal artery - a branch of the middle meningeal artery which passes retrogradely along the greater superficial petrosal nerve.

3.                stylomastoid artery - a branch of the occipital artery, which pases retrogradely into the stylomastoid foramen.

The labyrinthine segment is the most vulnerable to ischaemia as the connections between the labyrinthine artery and superficial petrosal artery are very tenuous, with each artery essentially being end arteries.

  The motor part supplies somatic motor fibers to the muscles of the face, scalp, and auricle, the Buccinator and Platysma, the Stapedius, the Stylohyoideus, and posterior belly of the Digastricus; it also contains some sympathetic motor fibers which constitute the vasodilator nerves of the submaxillary and sublingual glands, and are conveyed through the chorda tympani nerve. These are preganglionic fibers of the sympathetic system and terminate in the submaxillary ganglion and small ganglia in the hilus of the submaxillary gland. From these ganglia postganglionic fibers are conveyed to these glands. The sensory part contains the fibers of taste for the anterior two-thirds of the tongue and a few somatic sensory fibers from the middle ear region. A few splanchnic sensory fibers are also present.

image788

Plan of the facial and intermediate nerves and their communication with other nerves.

 

  The motor root arises from a nucleus which lies deeply in the reticular formation of the lower part of the pons. This nucleus is situated above the nucleus ambiguus, behind the superior olivary nucleus, and medial to the spinal tract of the trigeminal nerve. From this origin the fibers pursue a curved course in the substance of the pons. They first pass backward and medialward toward the rhomboid fossa, and, reaching the posterior end of the nucleus of the abducent nerve, run upward close to the middle line beneath the colliculus fasciculus. At the anterior end of the nucleus of the abducent nerve they make a second bend, and run downward and forward through the pons to their point of emergence between the olive and the inferior peduncle.

  The sensory root arises from the genicular ganglion, which is situated on the geniculum of the facial nerve in the facial canal, behind the hiatus of the canal. The cells of this ganglion are unipolar, and the single process divides in a T-shaped manner into central and peripheral branches. The central branches leave the trunk of the facial nerve in the internal acoustic meatus, and form the sensory root; the peripheral branches are continued into the chorda tympani and greater superficial petrosal nerves. Entering the brain at the lower border of the pons between the motor root and the acoustic nerve, the fibers of the sensory root pass into the substance of the medulla oblongata and end in the upper part of the terminal nucleus of the glossopharyngeal nerve and in the fasciculus solitarius.

image789

The course and connections of the facial nerve in the temporal bone.

 

  From their superficial attachments to the brain, the two roots of the facial nerve pass lateralward and forward with the acoustic nerve to the internal acoustic meatus. In the meatus the motor root lies in a groove on the upper and anterior surface of the acoustic nerve, the sensory root being placed between them.

  At the bottom of the meatus, the facial nerve enters the facial canal, which it traverses to its termination at the stylomastoid foramen. It is at first directed lateralward between the cochlea and vestibule toward the medial wall of the tympanic cavity; it then bends suddenly backward and arches downward behind the tympanic cavity to the stylomastoid foramen. The point where it changes its direction is named the geniculum; it presents a reddish gangliform swelling, the genicular ganglion (ganglion geniculi; geniculate ganglion; nucleus of the sensory root of the nerve)(789). On emerging from the stylomastoid foramen, the facial nerve runs forward in the substance of the parotid gland, crosses the external carotid artery, and divides behind the ramus of the mandible into branches, from which numerous offsets are distributed over the side of the head, face, and upper part of the neck, supplying the superficial muscles in these regions. The branches and their offsets unite to form the parotid plexus.

 

Branches of Communication.—The branches of communication of the facial nerve may be arranged as follows:

In the internal acoustic meatus………………

With the acoustic nerve.

At the genicular ganglion……………………

With the sphenopalatine ganglion by the greater superficial petrosal nerve.

With the otic ganglion by a branch which joins the lesser superficial petrosal nerve.

With the sympathetic on the middle meningeal artery.

In the facial canal……………………………

With the auricular branch of the vagus.

At its exit from the stylomastoid foramen……

With the glossopharyngeal.

With the vagus.

With the great auricular.

With the auriculotemporal.

Behind the ear………………………………

With the lesser occipital.

On the face…………………………………

With the trigeminal.

In the neck…………………………………

With the cutaneous cervical.

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  In the internal acoustic meatus some minute filaments pass from the facial to the acoustic nerve.

  The greater superficial petrosal nerve (large superficial petrosal nerve) arises from the genicular ganglion, and consists chiefly of sensory branches which are distributed to the mucous membrane of the soft palate; but it probably contains a few motor fibers which form the motor root of the sphenopalatine ganglion. It passes forward through the hiatus of the facial canal, and runs in a sulcus on the anterior surface of the petrous portion of the temporal bone beneath the semilunar ganglion, to the foramen lacerum. It receives a twig from the tympanic plexus, and in the foramen is joined by the deep petrosal, from the sympathetic plexus on the internal carotid artery, to form the nerve of the pterygoid canal which passes forward through the pterygoid canal and ends in the sphenopalatine ganglion. The genicular ganglion is connected with the otic ganglion by a branch which joins the lesser superficial petrosal nerve, and also with the sympathetic filaments accompanying the middle meningeal artery. According to Arnold, a twig passes back from the ganglion to the acoustic nerve. Just before the facial nerve emerges from the stylomastoid foramen, it generally receives a twig from the auricular branch of the vagus.

  After its exit from the stylomastoid foramen, the facial nerve sends a twig to the glossopharyngeal, and communicates with the auricular branch of the vagus, with the great auricular nerve of the cervical plexus, with the auriculotemporal nerve in the parotid gland, and with the lesser occipital behind the ear; on the face with the terminal branches of the trigeminal, and in the neck with the cutaneous cervical nerve.

 

Branches of Distribution.—The branches of distribution (788) of the facial nerve may be thus arranged:

With the facial canal…………………………..

Nerve to the Stapedius muscle.

Chorda tympani.

At its exit from the stylomastoid foramen………

Posterior auricular.

Digastric.

Stylohyoid.

On the face……………………………………

Temporal.

Zygomatic.

Buccal.

Mandibular.

Cervical.

  The Nerve to the Stapedius (n. stapedius; tympanic branch) arises opposite the pyramidal eminence (page 1042); it passes through a small canal in this eminence to reach the muscle.

image790

The nerves of the scalp, face, and side of neck.

 

  The Chorda Tympani Nerve is given off from the facial as it passes downward behind the tympanic cavity, about 6 mm. from the stylomastoid foramen. It runs upward and forward in a canal, and enters the tympanic cavity, through an aperture (iter chordæ posterius) on its posterior wall, close to the medial surface of the posterior border of the tympanic membrane and on a level with the upper end of the manubrium of the malleus. It traverses the tympanic cavity, between the fibrous and mucous layers of the tympanic membrane, crosses the manubrium of the malleus, and emerges from the cavity through a foramen situated at the inner end of the petrotympanic fissure, and named the iter chordæ anterius (canal of Huguier). It then descends between the Pterygoideus externus and internus on the medial surface of the spina angularis of the sphenoid, which it sometimes grooves, and joins, at an acute angle, the posterior border of the lingual nerve. It receives a few efferent fibers from the motor root; these enter the submaxillary ganglion, and through it are distributed to the submaxillary and sublingual glands; the majority of its fibers are afferent, and are continued onward through the muscular substance of the tongue to the mucous membrane covering its anterior two-thirds; they constitute the nerve of taste for this portion of the tongue. Before uniting with the lingual nerve the chorda tympani is joined by a small branch from the otic ganglion.

The Posterior Auricular Nerve (n. auricularis posterior) arises close to the stylo-mastoid foramen, and runs upward in front of the mastoid process; here it is joined by a filament from the auricular branch of the vagus, and communicates with the posterior branch of the great auricular, and with the lesser occipital. As it ascends between the external acoustic meatus and mastoid process it divides into auricular and occipital branches. The auricular branch supplies the Auricularis posterior and the intrinsic muscles on the cranial surface of the auricula. The occipital branch, the larger, passes backward along the superior nuchal line of the occipital bone, and supplies the Occipitalis.

The Digastric Branch (ramus digastricus) arises close to the stylomastoid foramen, and divides into several filaments, which supply the posterior belly of the Digastricus; one of these filaments joins the glossopharyngeal nerve.

  The Stylohyoid Branch (ramus stylohyoideus) frequently arises in conjunction with the digastric branch; it is long and slender, and enters the Stylohyoideus about its middle.

  The Temporal Branches (rami temporales) cross the zygomatic arch to the temporal region, supplying the Auriculares anterior and superior, and joining with the zygomaticotemporal branch of the maxillary, and with the auriculotemporal branch of the mandibular. The more anterior branches supply the Frontalis, the Orbicularis oculi, and the Corrugator, and join the supraorbital and lacrimal branches of the ophthalmic.

  The Zygomatic Branches (rami zygomatici; malar branches) run across the zygomatic bone to the lateral angle of the orbit, where they supply the Orbicularis oculi, and join with filaments from the lacrimal nerve and the zygomaticofacial branch of the maxillary nerve.

  The Buccal Branches (rami buccales; infraorbital branches), of larger size than the rest, pass horizontally forward to be distributed below the orbit and around the mouth. The superficial branches run beneath the skin and above the superficial muscles of the face, which they supply: some are distributed to the Procerus, joining at the medial angle of the orbit with the infratrochlear and nasociliary branches of the ophthalmic. The deep branches pass beneath the Zygomaticus and the Quadratus labii superioris, supplying them and forming an infraorbital plexus with the infraorbital branch of the maxillary nerve. These branches also supply the small muscles of the nose. The lower deep branches supply the Buccinator and Orbicularis oris, and join with filaments of the buccinator branch of the mandibular nerve.

  The Mandibular Branch (ramus marginalis mandibulæ) passes forward beneath the Platysma and Triangularis, supplying the muscles of the lower lip and chin, and communicating with the mental branch of the inferior alveolar nerve.

  The Cervical Branch (ramus colli) runs forward beneath the Platysma, and forms a series of arches across the side of the neck over the suprahyoid region. One branch descends to join the cervical cutaneous nerve from the cervical plexus; others supply the Platysma.

Greater petrosal nerve (preganglionic secretory fibers to the lacrimal glands, nasal glands and palatal glands) separates off from the geniculate ganglion, extends through the hiatus of the canal for the greater petrosal nerve, across the foramen lacerum and finally through the pterygoid canal to the pterygopalatine ganglion.

Chorda tympani carries preganglionic secretory fibers to the submandibular and sublingual glands and taste fibers to the anterior two third of the tongue. Taste (sensory) fibers contain peripheral axons of cells localized in geniculate ganglion. The central process of neurocytes of this ganglion terminate in nucleus of solitarius tract. Chorda tympani passes through the petrotympanic fissura and joints the lingual nerve (from the Vth cranial nerve), then its branches reach the tongue and parasympathetic submandibular and sublingual ganglia for innervating the same names salivary glands.

Facial nerve paralysis

·                     Clinical features

o         Facial asymmetry

o         Eyebrow droop

o         Loss of forehead & nasolabial folds

o         Drooping of corner of mouth

o         Uncontrolled tearing

o         Inability to close eye

o         Lips not held tightly together: Difficulty keeping food in mouth

o         Facial muscle atrophy (Late)

·                     Electrophysiology

o         EMG

§           Denervation

§           Synkinesis: Late

o         Blink reflex

§           Abnormal ipsilateral

o                            R1 (early, disynaptic)

o                            R2 (late multisynaptic) responses

§           Synkinesis (Late)

The VIIth cranial (facial) nerve is largely motor in function (some sensory fibres from external acoustic meatus, fibres controlling salivation and taste fibres from the anterior tongue in the chorda tympani branch). It also supplies the stapedius (so a complete nerve lesion will alter auditory acuity on the affected side). From the facial nerve nucleus in the brainstem, fibres loop around the VI nucleus before leaving the pons medial to VIII and passing through the internal acoustic meatus. It passes through the petrous temporal in the facial canal, widens to form the geniculate ganglion (taste and salivation) on the medial side of the middle ear, whence it turns sharply (and the chorda tympani leaves), to emerge through the stylomastoid foramen to supply all the muscles of facial expression, including the platysma.

Weakness of the muscles of facial expression and eye closure. The face sags and is drawn across to the opposite side on smiling. Voluntary eye closure may not be possible and can produce damage to the conjunctiva and cornea.

The most common system used for describing the degree of paralysis is the House-Brackmann scale, where 1 is normal power and 6 is total paralysis.[1]

It is important to identify whether the patient has an upper motor neurone (UMN) or lower motor neurone (LMN) lesion, to assist in identifying the cause.

Cerebrovascular accidents usually weaken voluntary movement, often sparing involuntary movements (eg, spontaneous smiling). The much rarer selective loss of emotional movement is called mimic paralysis and is usually due to a frontal or thalamic lesion.

XI Accessory nerve is a motor nerve, which has a ambiguus nucleus (cranial) and nucleus of accessory nerve (spinal nucleus). The accessory rootlets pass through the jugular and magnum foramen. Trunk of accessory nerve divides into internal branch and external branch. Internal branch joints vagus nerve, and an external branch reaches the sternocleidomastoid and trapezius muscles (innervating them).

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The accessory nerve consists of two parts: a cranial and a spinal.

1) The Cranial Part (ramus internus; accessory portion) is the smaller of the two. Its fibers arise from the cells of the nucleus ambiguus and emerge as four or five delicate rootlets from the side of the medulla oblongata, below the roots of the vagus. It runs lateralward to the jugular foramen, where it interchanges fibers with the spinal portion or becomes united to it for a short distance; here it is also connected by one or two filaments with the jugular ganglion of the vagus. It then passes through the jugular foramen, separates from the spinal portion and is continued over the surface of the ganglion nodosum of the vagus, to the surface of which it is adherent, and is distributed principally to the pharyngeal and superior laryngeal branches of the vagus. Through the pharyngeal branch it probably supplies the Musculus uvulae and Levator veli palatini. Some few filaments from it are continued into the trunk of the vagus below the ganglion, to be distributed with the recurrent nerve and probably also with the cardiac nerves.

2) The Spinal Part (ramus externus; spinal portion) is firm in texture, and its fibers arise from the motor cells in the lateral part of the anterior column of the gray substance of the medulla spinalis as low as the fifth cervical nerve. Passing through the lateral funiculus of the medulla spinalis, they emerge on its surface and unite to form a single trunk, which ascends between the ligamentum denticulatum and the posterior roots of the spinal nerves; enters the skull through the foramen magnum, and is then directed to the jugular foramen, through which it passes, lying in the same sheath of dura mater as the vagus, but separated from it by a fold of the arachnoid. In the jugular foramen, it receives one or two filaments from the cranial part of the nerve, or else joins it for a short distance and then separates from it again. As its exit from the jugular foramen, it runs backward in front of the internal jugular vein in 66.6 per cent. of cases, and behind in it 33.3 per cent. (Tandler). The nerve then descends obliquely behind the Digastricus and Stylohyoideus to the upper part of the Sternocleidomastoideus; it pierces this muscle, and courses obliquely across the posterior triangle of the neck, to end in the deep surface of the Trapezius. As it traverses the Sternocleidomastoideus it gives several filaments to the muscle, and joins with branches from the second cervical nerve. In the posterior triangle it unites with the second and third cervical nerves, while beneath the Trapezius it forms a plexus with the third and fourth cervical nerves, and from this plexus fibers are distributed to the muscle.

The Cranial part ( accessory portion) is the smaller of the two. Its fibers arise from the cells of the nucleus ambiguus and emerge as four or five delicate rootlets from the side of the medulla oblongata, below the roots of the vagus. It runs laterally to the jugular foramen, where it interchanges fibers with the spinal portion or becomes united to it for a short distance; here it is also connected by one or two filaments with the jugular ganglion of the vagus. It then passes through the jugular foramen, separates from the spinal portion and is continued over the surface of the ganglion nodosum of the vagus, to the surface of which it is adherent, and is distributed principally to the pharyngeal and superior laryngeal branches of the vagus. Through the pharyngeal branch it probably supplies the musculus uvulae and levator veli palatini. Some few filaments from it are continued into the trunk of the vagus below the ganglion, to be distributed with the recurrent nerve and probably also with the cardiac nerves.

 The Spinal part (spinal portion) is firm in texture, and its fibers arise from the ventral horn cells in the cord between C1 and C5. The fibres emerge from the cord laterally between the anterior and posterior spinal nerve roots to form a single trunk, which ascends into  the skull through the foramen magnum. It  then exits the skull through the jugular foramen, through which it passes, lying in the same sheath of dura mater as the vagus, but separated from it by a fold of the arachnoid.

·                     In the jugular foramen, it receives one or two filaments from the cranial part of the nerve, or else joins it for a short distance and then separates from it again.

·                     As it exits from the jugular foramen, it runs backwards then descends obliquely behind the digastric and stylohyoid muscles to the upper part of the sternocleidomastoid; it pierces this muscle, and courses obliquely across the posterior triangle of the neck, to end in the deep surface of the trapezius muscle.

·                     As it traverses the sternocleidomastoid it gives several filaments to the muscle, and joins with branches from the second cervical nerve. In the posterior triangle it unites with the second and third cervical nerves, while beneath the trapezius it forms a plexus with the third and fourth cervical nerves, and from this plexus fibers are distributed to the muscle. Most consider the cranial part of the eleventh cranial nerve to be functionally part of the vagus nerve.

Functions

The accessory nerve is responsible for the motor innervation of the sternocleidomastoid and trapezius muscles.

·                     The sternocleidomastoid acts in elevation of the thoracic cage and shoulder girdle, or, with fixation of the limb, will act in lateral flexion of the head to the shoulder on the same side and rotate the head to direct the chin upward to the opposite side.

·                     The trapezius muscle is one of several muscles that elevate the shoulder girdle and retract the girdle dorsally.

In anatomy, the accessory nerve is a nerve that controls specific muscles of the shoulder and neck. As part of it was formerly believed to originate in the brain, it is considered a cranial nerve. Based on its location relative to other such nerves, it is designated the eleventh of twelve cranial nerves, and is thus abbreviated CN XI.

Traditional descriptions of the accessory nerve divide it into two parts: a spinal part and a cranial part. But because the cranial component rapidly joins the vagus nerve and serves the same function as other vagal nerve fibers, modern descriptions often consider the cranial component part of the vagus nerve and not part of the accessory nerve proper. Thus in contemporary discussions of the accessory nerve, the common practice is to dismiss the cranial part altogether, referring to the accessory nerve specifically as the spinal accessory nerve.

The spinal accessory nerve provides motor innervation from the central nervous system to two muscles of the neck: the sternocleidomastoid muscle and the trapezius muscle. The sternocleidomastoid muscle tilts and rotates the head, while the trapezius muscle has several actions on the scapula, including shoulder elevation and adduction of the scapula.

Range of motion and strength testing of the neck and shoulders can be measured during a neurological examination to assess function of the spinal accessory nerve. Limited range of motion or poor muscle strength are suggestive of damage to the spinal accessory nerve, which can result from a variety of causes. Injury to the spinal accessory nerve is most commonly caused by medical procedures that involve the head and neck.

The accessory nerve is derived from the basal plate of the embryonic spinal segments C1–C6.

Like other cranial nerves, the spinal accessory nerve begins in the central nervous system and exits the cranium through a specialized hole (or foramen). However, unlike all other cranial nerves, the spinal accessory nerve begins outside the skull rather than inside. In particular, in the majority of individuals, the fibers of the spinal accessory nerve originate solely in neurons situated in the upper spinal cord. These fibers coalesce to form spinal rootlets, roots, and finally the spinal accessory nerve itself, which enters the skull through the foramen magnum, the large opening at the base of the skull. The nerve courses along the inner wall of the skull towards the jugular foramen, through which it exits the skull with the glossopharyngeal (CN IX) and vagus nerves (CN X). Owing to its peculiar course, the spinal accessory nerve is notable for being the only cranial nerve to both enter and exit the skull.

Traditionally, the accessory nerve is described as having a small cranial component that descends from the medulla oblongata and briefly connects with the spinal accessory component before branching off of the nerve to join the vagus nerve. A recent study of twelve subjects suggests that in the majority of individuals, this cranial component does not make any distinct connection to the spinal component; the roots of these distinct components were separated by a fibrous sheath in all but one subject.

Once the cranial component has detached from the spinal component, the spinal accessory nerve continues alone and heads posteriorly (backwards) and inferiorly (downwards) upon exiting the skull. In the neck, the accessory nerve crosses the internal jugular vein around the level of the posterior belly of digastric muscle. Masoud Saman et al. in a study of 84 necks  reported that in the anterior triangle of the neck the accessory nerve crossed the internal jugular vein anteriorly in 80% of necks, posteriorly in 19% and in the one case of internal jugular vein bifurcation, the nerve pierced the vein. The average distance traveled by nerve from base of skull to crossing the internal jugular vein was 2.38 cm. As it courses caudally, the nerve pierces the sternocleidomastoid muscle while sending it motor branches, then continues inferiorly until it reaches the trapezius muscle to provide motor innervation to its upper portion.

Origin

The fibers that form the spinal accessory nerve are formed by lower motor neurons located in the upper segments of the spinal cord. This cluster of neurons, called the spinal accessory nucleus, is located in the lateral horn of the spinal cord. This is in contrast to most other motor neurons, whose cell bodies are found in the spinal cord's anterior horn. The lateral horn of high cervical segments appears to be continuous with the nucleus ambiguus of the medulla oblongata, from which the cranial component of the accessory nerve is derived.

Classification

Among investigators there is disagreement regarding the terminology used to describe the type of information carried by the accessory nerve. As the trapezius and sternocleidomastoid muscles are derived from the branchial arches, some investigators believe the spinal accessory nerve that innervates them must carry branchiomeric (special visceral efferent, SVE) information.[6] This is in line with the observation that the spinal accessory nucleus appears to be continuous with the nucleus ambiguus of the medulla. Others, notably Haines, consider the spinal accessory nerve to carry general somatic efferent (GSE) information.[7] Still others believe it is reasonable to conclude that the spinal accessory nerve contains both SVE and GSE components.[8]

The trapezius muscle is tested by asking the patient to shrug their shoulders with and without resistance. A one-sided weakness is indicative of an injury to the spinal accessory nerve on the same side (termed ipsilateral) of the body being assessed. The sternocleidomastoid muscle is tested by asking the patient to turn their head to the left or right against resistance. Weakness in head-turning suggests injury to the contralateral spinal accessory nerve: a weak leftward turn is indicative of a weak right sternocleidomastoid muscle (and thus right spinal accessory nerve injury), while a weak rightward turn is indicative of a weak left sternocleidomastoid muscle (and thus left spinal accessory nerve).

Gross observation may identify other findings associated with spinal accessory nerve injury. Patients with spinal accessory nerve palsy may exhibit signs of lower motor neuron disease such as diminished muscle mass (atrophy) and fasciculations of the sternocleidomastoid and trapezius muscles.

http://l.yimg.com/a/i/edu/ref/ga/s/794.jpg 

The Cranial Part (ramus internus; accessory portion) is the smaller of the two. Its fibers arise from the cells of the nucleus ambiguus and emerge as four or five delicate rootlets from the side of the medulla oblongata, below the roots of the vagus. It runs lateralward to the jugular foramen, where it interchanges fibers with the spinal portion or becomes united to it for a short distance; here it is also connected by one or two filaments with the jugular ganglion of the vagus. It then passes through the jugular foramen, separates from the spinal portion and is continued over the surface of the ganglion nodosum of the vagus, to the surface of which it is adherent, and is distributed principally to the pharyngeal and superior laryngeal branches of the vagus. Through the pharyngeal branch it probably supplies the Musculus uvulæ and Levator veli palatini. Some few filaments from it are continued into the trunk of the vagus below the ganglion, to be distributed with the recurrent nerve and probably also with the cardiac nerves. The Spinal Part (ramus externus; spinal portion) is firm in texture, and its fibers arise from the motor cells in the lateral part of the anterior column of the gray substance of the medulla spinalis as low as the fifth cervical nerve. Passing through the lateral funiculus of the medulla spinalis, they emerge on its surface and unite to form a single trunk, which ascends between the ligamentum denticulatum and the posterior roots of the spinal nerves; enters the skull through the foramen magnum, and is then directed to the jugular foramen, through which it passes, lying in the same sheath of dura mater as the vagus, but separated from it by a fold of the arachnoid. In the jugular foramen, it receives one or two filaments from the cranial part of the nerve, or else joins it for a short distance and then separates from it again. As its exit from the jugular foramen, it runs backward in front of the internal jugular vein in 66.6 per cent. of cases, and behind in it 33.3 per cent. (Tandler). The nerve then descends obliquely behind the Digastricus and Stylohyoideus to the upper part of the Sternocleidomastoideus; it pierces this muscle, and courses obliquely across the posterior triangle of the neck, to end in the deep surface of the Trapezius. As it traverses the Sternocleidomastoideus it gives several filaments to the muscle, and joins with branches from the second cervical nerve. In the posterior triangle it unites with the second and third cervical nerves, while beneath the Trapezius it forms a plexus with the third and fourth cervical nerves, and from this plexus fibers are distributed to the muscle.

Function

The nerve functions to control the sternocleidomastoid and trapezius muscles. The thoracic branches of the spinal accessory nerve are matched to vagal innervation in early embyrologic development of the mammalian heart.

Injury

Injury to the spinal accessory nerve can cause an accessory nerve disorder or spinal accessory nerve palsy, which results in diminished or absent function of the sternocleidomastoid muscle and upper portion of the trapezius muscle.

The distal part of the spinal accessory nerve is most susceptible to injury. Throughout much of its course, the nerve is protected from injury by the muscles it innervates. It is in the interval between protection from these muscles, which corresponds to the distal part of the nerve, that the spinal accessory nerve is most vulnerable to injury.

Assessment of function

As physical examination cannot directly assess the functioning of nerves, assessment of spinal accessory nerve function is usually done indirectly. This is often accomplished through gross observation, range of motion testing, and strength testing, with specific attention to the trapezius and sternocleidomastoid muscles which are innervated by the spinal accessory nerve.

XII Hypoglossal nerve is a motor nerve, which has an motor nucleus in hypoglossall trigone of rhomboid fossa. Nerve exits from myelencephalon by numerous rootlets in furrow between pyramid and olive, and passes through the of hypoglossal canal. Hypoglossal nerve runs into submandibular triangle (it borders lingual triangle here) and enters into tongue thickness, where disintegrates on lingual branches, that innervate all tongue muscles (Extrinsic: Genioglossus, Hyoglossus and Styloglossus muscles; and intrinsic: Superior Longitudinal, Inferior Longitudinal, Transverse and Vertical muscles).

The nerve arises from the hypoglossal nucleus and emerges from the medulla oblongata in the preolivary sulcus separating the olive and the pyramid. It then passes through the hypoglossal canal. On emerging from the hypoglossal canal, it gives off a small meningeal branch and picks up a branch from the anterior ramus of C1. It spirals behind the vagus nerve and passes between the internal carotid artery and internal jugular vein lying on the carotid sheath. After passing deep to the posterior belly of the digastric muscle, it passes to the submandibular region, passes lateral to the Hyoglossus muscle, and inferior to the lingual nerve to reach and efferently innervate the tongue.

It supplies motor fibres to all of the muscles of the tongue, except the palatoglossus muscle, which is innervated by the vagus nerve (cranial nerve X) or, according to some classifications, by fibres from the glossopharyngeal nerve (cranial nerve IX) that "hitchhike" within the vagus. It controls tongue movements of speech, food manipulation, and swallowing.

The hypoglossal nerve is derived from the basal plate of the embryonic medulla oblongata.

Function

Swallowing to clear mouth of saliva and other involuntary activities completed by the tongue are controlled by the hypoglossal nerve; however, most functions are voluntary. Voluntary control requires conscious thought and nerve pathways occur in the corticobulbar region in the spinal cord.

The function of the hypoglossal nerve in manipulation for speech contributes to learning languages. Many languages require specific and sometimes unusual uses to create the desired sounds, hence why adults learning a new language may have trouble adjusting to the new movements.

Testing the hypoglossal nerve

To test the function of the nerve, a person is asked to poke out his/her tongue. If there is a loss of function on one side (unilateral paralysis), the tongue will point toward the affected side, due to unopposed action of the genioglossus muscle (which pulls the tongue forward) on the side of the tongue that is usually innervated. This is the result of a lower motor neuron lesion (the damaged neuron directly innervates the skeletal muscle), and can lead to fasciculations and atrophy of the tongue.

The strength of the tongue can be tested by getting the person to poke the inside of his/her cheek, and feeling how strongly he/she can push a finger pushed against the cheek - a more elegant way of testing than directly touching the tongue.

The tongue can also be looked at for signs of lower motor neuron disease, such as fasciculation and atrophy.

Paralysis/paresis of one side of the tongue results in ipsilateral curvature of the tongue (apex toward the impaired side of the mouth); i.e., the tongue will move toward the affected side.

Cranial Nerve XII is innervated by the contralateral cortex, so a purely upper motor neuron (cortex) lesion will cause the tongue to deviate away from the side of the cortical lesion. Additionally, the fasciculations and atrophy seen in lower motor neuron lesions are not present.

Weakness of the tongue is displayed as a slurring of speech. The tongue may feel "thick", "heavy", or "clumsy." Lingual sounds (i.e., l's, t's, d's, n's, r's, etc.) are slurred and this is obvious in conversation.[4]

Uses in nerve repair

Facial nerve paralysis is a difficult situation to fix, but new cranial nerve substitution techniques allow for some usage to be restored, to include hypoglossal-facial anastomosis.

This procedure is considered the standard for reanimating the face when the proximal end of the facial nerve is not available, but the peripheral system is still viable. There are two options:

·                     Hypoglossal nerve completely transected and connected to facial nerve.

·                     Hypoglossal nerve partially transected and connected to facial nerve. This may be accomplished with interposition cable grafts or jump grafts. An advantage of partial transection is minimizing tongue weakness and purported decrease in synkinesis. There are disadvantages though since there are then fewer nerve cells to drive the movement of features in the face.

Hypoglossal nerve gives off the descending ramus which joins with descending branch from cervical plexus forming ansa cervicalis. It gives off the motor branches innervating infrahyoid muscles: sternohyoid, sternothyroid, omothyroid and thyrohyoid. The hypoglossal nerve is the motor nerve of the tongue. Its fibers arise from the cells of the hypoglossal nucleus, which is an upward prolongation of the base of the anterior column of gray substance of the medulla spinalis. This nucleus is about 2 cm. in length, and its upper part corresponds with the trigonum hypoglossi, or lower portion of the medial eminence of the rhomboid fossa. The lower part of the nucleus extends downward into the closed part of the medulla oblongata, and there lies in relation to the ventro-lateral aspect of the central canal. The fibers run forward through the medulla oblongata, and emerge in the antero-lateral sulcus between the pyramid and the olive. The rootlets of this nerve are collected into two bundles, which perforate the dura mater separately, opposite the hypoglossal canal in the occipital bone, and unite together after their passage through it; in some cases the canal is divided into two by a small bony spicule.

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The nerve descends almost vertically to a point corresponding with the angle of the mandible. It is at first deeply seated beneath the internal carotid artery and internal jugular vein, and intimately connected with the vagus nerve; it then passes forward between the vein and artery, and lower down in the neck becomes superficial below the Digastricus. The nerve then loops around the occipital artery, and crosses the external carotid and lingual arteries below the tendon of the Digastricus. It passes beneath the tendon of the Digastricus, the Stylohyoideus, and the Mylohyoideus, lying between the last-named muscle and the Hyoglossus, and communicates at the anterior border of the Hyoglossus with the lingual nerve; it is then continued forward in the fibers of the Genioglossus as far as the tip of the tongue, distributing branches to its muscular substance.   

The descending ramus (ramus descendens; descendens hypoglossi), long and slender, quits the hypoglossal where it turns around the occipital artery and descends in front of or in the sheath of the carotid vessels; it gives a branch to the superior belly of the Omohyoideus, and then joins the communicantes cervicales from the second and third cervical nerves; just below the middle of the neck, to form a loop, the ansa cervicalis. From the convexity of this loop branches pass to supply the Sternohyoideus, the Sternothyreoideus, and the inferior belly of the Omohyoideus. According to Arnold, another filament descends in front of the vessels into the thorax, and joins the cardiac and phrenic nerves. The Thyrohyoid Branch (ramus thyreohyoideus) arises from the hypoglossal near the posterior border of the hyoglossus; it runs obliquely across the greater cornu of the hyoid bone, and supplies the Thyreohyoideus muscle. The Muscular Branches are distributed to the Styloglossus, Hyoglossus, Geniohyoideus, and Genioglossus. At the under surface of the tongue numerous slender branches pass upward into the substance of the organ to supply its intrinsic muscles.

Prepared by

Galytsa-Harhalis O.Ya.

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